add Rocksdb read 'cache keys shard bits' from the configuration file

conf/pika.conf

@@ -142,6 +142,10 @@ max-bytes-for-level-multiplier : 10
 # block-size: 4096
 # block LRU cache, default 8M, 0 to disable
 # block-cache: 8388608
+# num-shard-bits default -1, the number of bits from cache keys to be use as shard id.
+# The cache will be sharded into 2^num_shard_bits shards.
+# /~https://github.com/EighteenZi/rocksdb_wiki/blob/master/Block-Cache.md#lru-cache
+# num-shard-bits: -1
 # whether the block cache is shared among the RocksDB instances, default is per CF
 # share-block-cache: no
 # whether or not index and filter blocks is stored in block cache

include/pika_conf.h

@@ -73,6 +73,7 @@ class PikaConf : public slash::BaseConf {
   int max_bytes_for_level_multiplier()              { RWLock l(&rwlock_, false); return max_bytes_for_level_multiplier_; }
   int64_t block_size()                              { RWLock l(&rwlock_, false); return block_size_; }
   int64_t block_cache()                             { RWLock l(&rwlock_, false); return block_cache_; }
+  int64_t num_shard_bits()                          { RWLock l(&rwlock_, false); return num_shard_bits_; }
   bool share_block_cache()                          { RWLock l(&rwlock_, false); return share_block_cache_; }
   bool cache_index_and_filter_blocks()              { RWLock l(&rwlock_, false); return cache_index_and_filter_blocks_; }
   bool pin_l0_filter_and_index_blocks_in_cache()    { RWLock l(&rwlock_, false); return pin_l0_filter_and_index_blocks_in_cache_; }
@@ -342,6 +343,7 @@ class PikaConf : public slash::BaseConf {
   int max_bytes_for_level_multiplier_;
   int64_t block_size_;
   int64_t block_cache_;
+  int64_t num_shard_bits_;
   bool share_block_cache_;
   bool cache_index_and_filter_blocks_;
   bool pin_l0_filter_and_index_blocks_in_cache_;

src/pika_conf.cc

@@ -448,6 +448,9 @@ int PikaConf::Load()
     block_cache_ = 8 * 1024 * 1024;
   }
 
+  num_shard_bits_ = -1;
+  GetConfInt64("num-shard-bits", &num_shard_bits_);
+
   std::string sbc;
   GetConfStr("share-block-cache", &sbc);
   share_block_cache_ = (sbc == "yes") ? true : false;

src/pika_server.cc

@@ -1657,7 +1657,7 @@ void PikaServer::InitBlackwidowOptions() {
     bw_options_.table_options.no_block_cache = true;
   } else if (bw_options_.share_block_cache) {
     bw_options_.table_options.block_cache =
-      rocksdb::NewLRUCache(bw_options_.block_cache_size);
+      rocksdb::NewLRUCache(bw_options_.block_cache_size, g_pika_conf->num_shard_bits());
   }
 
   // For Blackwidow small compaction